Osteoporosis is a major health care problem. However, the currently available therapeutic agents are associated with a variety of side effects and show only moderate efficacy. Interleukin-6 (IL-6) plays a major role in the activation of immature bone resorbing cells. IL-6 is produced by bone forming cells and its transcription is inhibited by estrogen. Therefore, targeting IL-6 gene expression is a novel approach for the development of anti-osteoporotic drugs. Signal Pharmaceuticals, Inc. intends to develop therapeutics for treatment of osteoporosis utilizing our expertise in intracellular signaling and transcriptional regulation. Our research approach is focused on inhibiting bone resorption with small molecules that act upon novel targets through novel mechanisms. Two screening projects have been initiated. The first is based upon suppressing osteoblast production of IL-6 by inhibiting the transcriptional regulators of IL-6, C/EBPbeta and NF-kappaB in the presence of estrogen receptor. The second project involves screening for ER-independent IL-6 inhibitors. High throughput, automated cell-based screens have been established to identify such compounds. Hits from these screens will be tested in secondary assays for cytotoxicity, specificity and selectivity. A human osteoblast/osteoclast co-culture model was developed that mimics the physiological environment of bone. This systems will be used to measure the efficacy of confirmed screening hits on osteoclast activation, bone resorption, and to validate novel targets. The ultimate goal is to develop drugs for the treatment of osteoporosis. Towards this goal we will screen for compounds that inhibit IL-6 gene expression. We established whole cell screening assays and follow-up assays including a human osteoblast/osteoclast co-culture system.